In many situations it is necessary to write information on photographic film after the film has been exposed and developed. Such situations arise in the motion picture industry in dubbing or reprinting cinematic films and in other industries where photographic film or microfilm are cataloged after processing.
For example, a typical situation occurs after a given cinematic film is received with its original sound track which contains the music as well as the spoken dialogue. When the language used is to be substituted by another one, there has first to be prepared a translation both according to the content of the dialogue, and also according to the number of syllables spoken, as otherwise a strange and unnatural effect is obtained.
In the present state of the recording art there are several methods for applying the new dialogue to the existing cinematic film. The first step in all prior art methods is to record the translated dialogue with a audio magnetic tape recorder. Well-known methods are used to synchronize the recorded dialogue to the actor's lip movements in the existing film. The resulting audio tape is normally called the new magnetic dialogue.
The new magnetic dialogue is now mixed with prerecorded, synchronized music and special sound effects in a well-known manner and re-recorded creating a composite final mix tape.
In order to prepare a commerical cinematic film including a picture and synchronized audio track, the audio signal on the final mix tape is transferred to the cinematic film by means of one of several methods.
One early methods was to use a composite film which had a magnetic sound track on the edge of a normal cinematic copy film. The audio information could then be directly recorded on the film from the final mix tape either before or after the film had been exposed. This method was commercially impractical because the magnetic sound track could easily be erased or damaged during handling or distribution, and the magnetic sound track could not be read by most existing projection equipment.
Another prior art method was to prepare an optical sound track with the final mix audio information by photographically exposing the optical sound track prior to processing of the film by means of a process called electroprinting. This process involved exposing the emulsion directly on the copy print stock by means of a light source passing through a narrow, variable-area slit located in front of the sound track area on the film. The area of the slit is modulated by the recorded audio information by means of a moving wedge which is driven by the audio signal. The problem with the electroprint system was that it could not produce a optical sound track with a satisfactory quality because the quality of the track depended on a number of variables which affected the contrast of the resulting track. Many of these variables could not be accurately controlled such as, processor contrast control, developer formula, temperature and exposure time. In addition the quality of the finished optical track required a fine grain, high-contrast emulsion and such an emulsion was not ordinarily used in the picture area of either positive or negative cinematic copy film.
In order to avoid some of the problems with the electroprint process multiple step processing procedures were used. In one procedure the picture area of the copy print film is exposed and developed. The sound track area is then recoated with a special fine grain, high-contrast emulsion. The optical sound track is then exposed and the sound track emulsion is then developed separately from the picture area. Due to the special treatment required, this method did not produce predictable results and the resulting sound tracks were not of high quality. Consequently the process is not used any longer.
Another process used to transfer the optical information to the photographic film is called optical printing on internegative film. In order to use the internegative process with normal copy film, the sound track is applied to the photographic film in two steps. First the magnetic track is tranferred and exposed on special film which has a fine grain and high contrast emulsion. The sound information is exposed in the optical track area but the film remains clear in the picture area. The original negative picture is separately printed on another negative film (the internegative) leaving a clear optical track area. Finally, the optical track and the internegative picture image are printed onto positive copy stock by contact printing to produce the cinematic film answer print.
Two methods have commonly been used with the internegative process to convert the sound information into an optical track. In one method, called the variable density method, the optical track emulsion is exposed by means of a light passing through a narrow slit in front of the sound track area of the film. the intensity of the light is varied by modulating the light source by the audio information. The problem with the variable density method is that it could not produce sound tracks of predictable quality since the resulting optical track had a continuous grey-scale ranging from clear to opaque. Thus, the quality of the processed track depends on proper exposure and various processing variables as well as fine-grain film.
The second method of converting the audio information to an optical sound track is the variable area method. The variable area method also involves exposing the emulsion by means of a light source passing through a small slit located in front of the film. However, in the variable area process the intensity of the light source is kept constant and the area of the slit is changed by a moving wedge controlled by the audio information. The resulting sound track can also be read by conventional projection equipment, but also requires high contrast emulsion on the optical track of copy print to produce a high-quality track.
Because the internegative process with variable area conversion produces a high-quality optical track on normal copy stock, it is the current method used to process copies. But, due to the necessity of a synchronizer to synchronize the printing of the optical track with the picture negative, the method is cumbersome and expensive. Furthermore it is useful only for a certain number of copies at least, as otherwise it is too expensive. Generally nowadays such films can be prepared only at the original film studios and the availability of the dubbed films depends on the capacities of such studios.